SD Card Speed only 10MB/s

Hello Folks.

First, the offending device is not a Rock Pi X but a handheld with the same Processor than the Rock Pi X has, the Intel z8350. The device is running Windows 10 Pro, and the problem is, that the SD card in the builtin reader gets only accessed with 10MB/s read and write. I tried several SD Cards all of them were from Sandisk, a Extreme Pro, a Ultra, and a High endurance. None of them works faster than 10MB/s, even if the cards itself should be ways faster.

Does anyone here know what causes this problem? I think the controller doesnt switch from standard mode to SDR104 mode, but I am not sure if its this, and when its is, why it doesnt switch to SDR104.

I Hope someone here has experience with the z8350 SOC, so someone here can help me.

Kind regards